Guided microfluidics by electromagnetic capillary focusing

As fluid channel sizes are reduced, nonspecific binding to channel walls and particle clogging of microchannels present key obstacles thus far limiting the application of microfluidic lab-on-a-chip technologies. Here we show how combining applied electric or magnetic fields with the increasing surface tension effects inherent in channel miniaturization can guide particle flow and prevent adhesion to channel walls. We demonstrate effective two-dimensional particle focusing within arbitrary channel geometries that prevents adhesion, allowing accurate control of Poiseuille flow effects, and acts as either a robust particle accumulator or a separator. (C) 2002 American Institute of Physics.